Blade arrangement of a gas turbine

ABSTRACT

A blade arrangement of a gas turbine, with at least one blade which in the radial direction projects into a hot gas passage arranged concentrically to an axis, and terminates in a blade tip which with a clearance lies opposite a heat shield which delimits the hot gas passage. The blade and the heat shield are movable in relation to each other in the circumferential direction, and the blade tip and the heat shield are covered with coatings, which enable a directed cutting of the blade tip into the heat shield. By such a blade arrangement, a reduction of the clearance as a result of cutting in is simply achieved by the heat shield having a porous thermal barrier coating as an outer, abradable coating, and by the blade tip being provided with a homogenous, metallic cover coating.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No.PCT/EP2009/060387 filed Aug. 11, 2009, which claims priority to SwissPatent Application No. 01285/08, filed Aug. 15, 2008, the entirecontents of all of which are incorporated by reference as if fully setforth.

FIELD OF INVENTION

The present invention relates to the field of gas turbine technology inthat it refers to a blade arrangement of a gas turbine.

BACKGROUND

For the efficiency of a gas turbine, it is of great importance,especially in the turbine section in which the hot gases from thecombustion chamber are expanded, to minimize as far as possible the gapswhich occur in the region of the blading between the bladed, rotatingrotor and the encompassing stator.

In the simplest case, as is reproduced in FIG. 1 with reference to theblade arrangement 10, no special measures are adopted for optimizing thegap width. The rotor blades 11 which project radially into the hot gaspassage 13 of the gas turbine and rotate around the axis 16, terminatein a blade tip 27 which is provided with a first cover coating 15 andwhich with a clearance 25 lies opposite a heat shield 12 which forms theouter wall 26 of the hot gas passage 13 and is provided with a secondcover coating 14. The cover coatings 14 and 15, which may compriseMCrAlY, for example, protect the components 11 and 12 against thedamaging effects of the hot gases in the hot gas passage 13, especiallyagainst undesirable oxidation. The blade arrangement 10 of FIG. 1 is notdesigned for cutting of the blade tips 27 into the heat shield 12. Theclearance 25 between the blade tips 27 and the heat shield 12 makesallowance for the different thermal expansions and is thereforecomparatively large in order to avoid rubbing of the components duringoperation.

In order to be able to reduce the clearance 25, blade arrangements 20according to FIG. 2 have been proposed (see, for example, EP-A2-1 312760 or US-A1-2008166225), in which abrasive bodies (grains) 21 (forexample consisting of cubic boron nitride cBN), which are embedded in acarrier layer 19 and with which the blade tip 27 can cut into anabradable thermal barrier coating (TBC) 18 on the oppositely disposedheat shield 12 during operation, are arranged on the blade tip 27 of therotor blades. A coating of metallic MCrAlY, for example, can be used asa carrier layer 19 for the abrasive bodies 21 and also as an adhesioncoating 17 beneath the thermal barrier coating 18.

The abrasive coating 19, 21 of such a blade arrangement is of acomparatively complex construction as a result of the embedded abrasivebodies and is therefore costly in production. The aim, however, wouldhave to be to create a comparable cutting-in behavior without a specialabrasive coating having to be provided on the blade tip.

SUMMARY

The present disclosure is directed to a blade arrangement of a thermalturbomachine with at least one blade, which projects in the radialdirection into a passage which is arranged concentrically to an axis andis exposed to throughflow by hot gas. The at least one blade terminatesin a blade tip which with a clearance lies opposite a heat shield whichdelimits the passage. The blade and the heat shield are movable inrelation to each other in a circumferential direction, and the blade tipand the heat shield are covered with coatings which enable a directedcutting of the blade tip into the heat shield, the heat shield has aporous thermal barrier coating as an outer, abradable coating, and theblade tip is provided with a homogenous, metallic cover coating.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall subsequently be explained in more detail based onexemplary embodiments in conjunction with the drawings. In the drawings

FIG. 1 shows in a greatly simplified view an earlier blade arrangementwithout the possibility of cutting in;

FIG. 2 shows in a view comparable to FIG. 1 another earlier bladearrangement with a special abradable coating on the blade tip, and

FIG. 3 shows in a view comparable to FIG. 1 a blade arrangement intendedfor cutting in, with a simple cover coating on the blade tip accordingto an exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Introduction to theEmbodiments

The invention should provide a remedy in this case. It is therefore theobject of the invention to disclose a blade arrangement which avoids thedisadvantages of known blade arrangements and with a simultaneouslysimple construction enables a significant reduction of the clearancebetween the blade tips and the oppositely disposed stator-side elements.

It is preferable for the heat shield to have a porous thermal barriercoating as an outer, abradable coating and for the blade tip to beprovided simply with a homogenous metallic cover coating. The porousthermal barrier coating enables the blade tip, which is covered by thecover coating, to cut into the heat shield even without special abrasivebodies or abrasive coating and so to optimally minimize the clearancebetween blade tip and oppositely disposed heat shield.

The blade is essentially a rotor blade or a stator blade of a thermalturbomachine, in particular a gas turbine, wherein in the case of astator blade a heat shield, which is fastened on the rotor, liesopposite the blade tip. According to a preferred embodiment, the bladeis a rotor blade which rotates around the axis, whereas the heat shieldis installed on the stator of the gas turbine in a fixed manner.

In another embodiment of the invention, the thermal barrier coating is aporous ceramic coating, in particular comprising YSZ. In this case, theporosity of the thermal barrier coating is preferably more than 20%.

An adhesion coating, particularly comprises MCrAlY, is advantageouslyarranged between the heat shield and the thermal barrier coating.

The metallic cover coating preferably comprises MCrAlY.

In a further embodiment, the rotor blade is part of the firstrotor-blade row in the turbine section of the gas turbine.

DETAILED DESCRIPTION

In FIG. 3, a preferred exemplary embodiment for a blade arrangement 30according to the invention is reproduced. In the example, a heat shield12, with a clearance 25, again lies opposite a rotor blade 11 which hasthe blade tip 27 and is rotatable around the axis 16 of the gas turbine.The clearance 25, and consequently the efficiency of the turbine, areoptimized by the blade tip 27 cutting into the coating 22, 23 of theheat shield 12 (in FIG. 3, the possible cutting-in region 28 on the heatshield is indicated by means of a broken line).

As a coating which is to be abraded during the cutting in, provision ismade on the heat shield 12 for a thermal barrier coating 23 which isconnected to the substrate of the heat shield 12 via an adhesion coating22 which lies in between. As an adhesion coating 22, provision maycustomarily be made for a metallic, anti-oxidation coating comprisingMCrAlY.

In trials, it has now been proved that cutting of the blade tip into thethermal barrier coating 23 is possible even without a special abrasivecoating on the blade tip 27 and leads to good results if the thermalbarrier coating 23—without losing its thermal properties—is to beslightly abraded to an adequate degree. This can be achieved by a porousthermal barrier coating 23 being used.

In this case, a porous ceramic coating, which in particular may compriseYSZ (yttrium oxide stabilized zirconium), is especially suitable as athermal barrier coating 23, wherein the porosity is created for exampleby means of embedded polymers which are subsequently heated. It has beenproved to be advantageous in this case if the porosity of the thermalbarrier coating is more than 20%, that is to say lies within the rangeof 22-24%, for example.

In the case of such a porous thermal barrier coating 23, the abrasion onthe blade tip 27 during cutting in, in relation to the depth of thecutting-in region 28, is comparatively small so that a special abrasivecoating on the blade tip 27 can be dispensed with. It suffices,therefore, if the blade tip 27 is covered with a homogenous covercoating 24 (without abrasive bodies) comprising MCrAlY, which isprovided anyway as a protective coating against oxidation of the bladematerial.

In this way, special provisions do not need to be made on the blade 11for cutting in, as a result of which, production of the blade 11 issubstantially simplified.

List of Designations

-   10, 20, 30 Blade arrangement (gas turbine)-   11 Rotor blade-   12 Heat shield-   14 Hot gas passage-   14, 15, 24 Cover coating-   16 Axis-   17, 22 Adhesion coating-   18, 23 Thermal barrier coating (TBC)-   19 Carrier layer-   21 Abrasive bodies-   25 Clearance-   26 Wall (hot gas passage)-   27 Blade tip-   28 Cutting-in region

1. A blade arrangement (30) of a thermal turbomachine with at least oneblade (11), which projects in the radial direction into a passage (13)which is arranged concentrically to an axis (16) and is exposed tothroughflow by hot gas, the at least one blade terminates in a blade tip(27) which with a clearance (25) lies opposite a heat shield (12) whichdelimits the passage (13), wherein the at least one blade (11) and theheat shield (12) are movable in relation to each other in acircumferential direction, and the blade tip (27) and the heat shield(12) are covered with coatings (22, 23, 24) which enable a directedcutting of the blade tip (27) into the heat shield (12), the heat shield(12) has a porous thermal barrier coating (23) as an outer, abradablecoating, and the blade tip (27) is provided with a homogenous, metalliccover coating (24).
 2. The blade arrangement as claimed in claim 1,wherein the thermal turbomachine is a gas turbine, the at least oneblade is a rotor blade (11) which rotates around the axis (16), and theheat shield (12) is installed on a stator of the gas turbine in a fixedmanner.
 3. The blade arrangement as claimed in claim 1, wherein thethermal barrier coating (23) is a porous ceramic coating, comprisingYSZ.
 4. The blade arrangement as claimed in claim 3, wherein a porosityof the thermal barrier coating (23) is more than 20%.
 5. The bladearrangement as claimed in claim 3, wherein an adhesion coating (22),comprising MCrAlY, is arranged between the heat shield (12) and thethermal barrier coating (23).
 6. The blade arrangement as claimed inclaim 1, wherein the metallic cover coating (24) comprises MCrAlY. 7.The blade arrangement as claimed in claim 2, wherein the rotor blade(11) is part of a first rotor-blade row in a turbine section of the gasturbine.
 8. The blade arrangement as claimed in claim 2, wherein thethermal barrier coating (23) is a porous ceramic coating, comprisingYSZ.
 9. The blade arrangement as claimed in claim 8, wherein a porosityof the thermal barrier coating (23) is more than 20%.
 10. The bladearrangement as claimed in claim 8, wherein an adhesion coating (22),comprising MCrAlY, is arranged between the heat shield (12) and thethermal barrier coating (23).
 11. The blade arrangement as claimed inclaim 2, wherein the metallic cover coating (24) comprises MCrAlY.